To control compliance of vehicles moving in a stream with a speed limit and automatically record violations, it is necessary to measure the speed and coordinates of a vehicle and, in the case of a speed limit violation, identify it with a required, rather high probability. Speed is generally measured by radars, whose principle of speed measurement is based on the Doppler effect, or by laser devices (lidars), whose principle of speed measurement is based on an assessment of the time intervals between emitted and received (as reflected from the vehicle) pulses, followed by speed calculation. These devices provide reliable metrological data on vehicle speeds. In speed monitoring, the vehicle coordinates are not determined but as a rule are set, i.e. a radar or a lidar measures the vehicle speed in a predetermined zone of control, whose size is comparable to that of a vehicle. In most reported cases, the vehicle is identified by its state registration (license) plate, which is read out by a video camera in the same zone of control and recognized by special software installed in the monitoring unit (for example, see the application WO9946613 IPC6, G01S 13/00, G08G 1/052, 1/054 issued on Sep. 6, 1999; CN1707545 IPC7 G08G 1/052, 1/054 issued on Dec. 14, 2005).
There are known methods and devices for determining the speed and coordinates using video cameras and sensor systems embedded in the roadway, where cameras are used to record the speed-violating vehicle (see, e.g., patent EP1513125 IPC7 G08G 1/017, 1/04, 1/054 issued on Mar. 9, 2005 and international application WO2005/062275 IPC7 G08G 1/01, 1/052, 1/054 issued on Jul. 7, 2005).
The drawbacks of these speed compliance monitoring systems are the specific requirements for the climatic conditions of their use (no snow and sub-zero temperatures). The above systems can record speed violations only at a road section situated between the sensors. Moreover, it is recommended to narrow the road section close to the distance between vehicle axes in order to measure the speed of a speed-violating vehicle more accurately.
There exists a speed measurement method where a selected road section is continuously recorded by a panoramic video camera (for example, see EP 1744 292 IPC7 G08G 1/04, 1/052, 1/054, G06 T7/00 issued on Jul. 10, 2006). The speed calculation is based on the distance between two fixed positions of the vehicle in two frames recorded by this video camera and on the time interval between these frames. The video camera is calibrated against four vertexes of a rectangle which are actually marked on the road surface at known distances. The detected speed violator is recorded by another camera capable of providing a higher definition video frame. The main disadvantage of this method and a device for its implementation according to the given patent is that, according to theoretical estimates and GOST R 50856-96 standard, the video camera is not the instrument intended to provide reliable metrological vehicle speed data, because it provides the vehicle speed calculation with an error depending on the video camera adjustment and calibration accuracy and on the dimensions of a moving vehicle.
One more method to detect speed-violating vehicles moving at exceeded speeds is known (see U.S. Pat. No. 6,696,978 IPC7 G08G 1/01, 1/052, 1/054, issued on Feb. 24, 2004). In accordance with this method, electromagnetic pulses are emitted by a radar or a laser locator (lidar) in the direction of the selected vehicle. Then reflected pulses are received, the vehicle speed is determined by a known method, and, if a speed limit is violated, a signal is generated to activate a video camera in order to capture a frame containing the license plate together with the measured speed value. The frame shall contain the following data: the measured speed value, the recognized license plate and other data required for vehicle identification. The received data are transmitted to the operational traffic control center for taking the appropriate measures against offences committed. The drawback of the method is that only one vehicle should be in the radar's coverage area. It means that the number of radars and video cameras should correspond to the number of traffic lanes, which significantly increases equipment and operation costs. Moreover the probability that the radar can simultaneously receive signals reflected from several vehicles is rather high. This increases the likelihood of the error of identifying a speed-violating vehicle which is not acceptable in cases where vehicles move in heavy traffic along several lanes. For instance, in accordance with patent GB 1211834 (IPC G01S 13/92, G08G 1/052, G08G 1/054, vehicle recording (photographing) is prohibited if there is more than one vehicle in the radar coverage area.
A method for determining the vehicle speed and coordinates together with the subsequent vehicle identification and automatic recording of traffic violations described in U.S. Pat. No. 6,266,627, IPC7, G08G 1/00, 1/052, 1/054, G01S 13/00 issued on Jul. 24, 2001 is quite similar to the proposed one in terms of its technical essence. In line with this method, electromagnetic pulses are emitted in the direction of vehicles moving along a road section, the reflected pulses are received, the distance and speed of the vehicle are calculated through comparison of the parameters of emitted and received pulses, and then the measured vehicle speed is compared with the maximum speed allowed in the given road section. If the speed limit is exceeded, a signal is generated to capture the license plate of a violating vehicle by a video camera; it is followed by the vehicle identification and automatic recording of speed limit violations. The traffic lane of the speed-violating vehicle is determined from the calculated distance.
The method also has the same drawback as the previous one does i.e. a high probability of the erroneous identification of a speed-violating vehicle. This can be explained as follows. For clarification, let's consider the real situation indicated in FIG. 1 and described in this patent. As is shown in FIG. 1, the radar beam is diverged at the angle of 4-5°. In fact, this is idealization used in theoretical calculations and corresponding to the −3 dB radiated power in the radar's main lobe. The real antenna radiation pattern, with regard to the main lobe power at −3 dB to approximately −20 dB level, is much wider and always contains side lobes as is shown in FIG. 1 of the additional materials pertaining to the prototype patent and is marked with hatching and pink color. There are signals reflected from vehicles in the aperture area of the antenna pattern (both in the main and side lobes) (see FIG. 1). All the vehicles, which fell within the arc with the radius R (a hatched green sector in FIG. 1), are at the same distance from the radar and hence all the pulses reflected from these vehicles will arrive at the radar simultaneously. As can be seen from FIG. 1, at least three vehicles moving along different traffic lanes are at the same distance from the radar and their returns will arrive at the same time but with different power. The power of received signals Pr is calculated by the formula:
      P    r    =                    P        t            ·              G        a                  ·          2                    ·              S        o                            4        ·                  π          3                ·                  R          4                           
where Pr is the power of received signals, Pt is the power of emitted signals, Ga2 is the squared antenna gain, So is the effective target area, R4 is the biquadrate of the target distance from the radar, which is the function of several varying parameters. Thus, the power of received signals Pr reflected from a vehicle with a small So (a small vehicle) at high Pt (the main lobe) can be commensurable with the power Pr of received signals reflected from a vehicle having large So (a big vehicle) but at low Pt (side lobes) which is moving along another traffic lane and is not exceeding the speed limit This may result in the false identification of a speed-violating vehicle.